I do not believe that you have a chance for domestic tickets. We bought around 13.000 domestic tickets in 2007, not even a chance even to discuss about.
It was/is much easier for intra Europe flights. We have certain "racetracks" and get very good deals for these (FRA-NYC, FRA-LHR, FRA-PAR), with certainly 500 flights on each route a year. However, once you ask they are very free to give you special deals on other routes too. I experienced that for DUS-LON and for FRA-HKG. For HKG I just needed two tickets, asked and got what I wanted, a nice D class deal. I believe, as soon as you hit a certain volume they provide you more or less with whatever you ask for - as long as it is not domestic.